Ignition and production of carbonaceous strata



United States Patent Ofifice 3,048,223 Patented Aug. 7, 1962 3,048,223IGNITIQN AND PRODUCTION OF (IONA- CEOUS STRATA Carl J. Helmers,Bartiesvilie, 91:121., assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Filed Dec. 29, W58, Ser. No. 783,206Claims. (Cl. 1166-11) This invention relates to an improved process forinitiating in situ combustion in a carbonaceous stratum and producingthe same by inverse injection of combustionsupporting gas.

In situ combustion in the recovery of hydrocarbons from undergroundstrata containing carbonaceous material is becoming more prevalent inthe petroleum industry. In this technique of production, combustion isinitiated in the carbonaceous stratum and the resulting combustion zoneis caused to move thru the stratum by either inverse or direct air drivewhereby the heat of combustion of a substantial proportion of thehydrocarbon in the stratum drives out and usually upgrades a substantialproportion of the unburned hydrocarbon material.

In the inverse air injection process upgrading of hydrocarbons bythermal and catalytic cracking is effected by driving the producedhydrocarbon material thru the hot rock or sand between the inverselytraveling combustion front and the production borehole.

The ignition of carbonaceous material in a stratum around a boreholetherein followed by injection of air thru the ignition borehole andrecovery of product hydrocarbons and combustion gas thru anotherborehole in the stratum is a direct air drive process for effecting insitu combustion and recovery of hydrocarbons from the. stratum. In thistype of operation the stratum usually plugs in front of the combustionzone because a heavy viscous liquid bank of hydrocarbon collects in thestratum in ad- Vance of the combustion zone which prevents movement ofair to the combustion process. To overcome this difficulty and to permitthe continued progress of the combustion zone thru the stratum, inverseair injection has been resorted to. By this technique, a combustion zoneis established around an ignition borehole by any suitable means and airis fed thru the stratum to the combustion zone from one or moresurrounding boreholes.

In situ combustion techniques are being applied to tar sands, shale,Athabasca sand and other strata in virgin state, to coal veins byfracturing, and to strata partially depleted by primary and evensecondary and tertiary recovery methods.

A problem in establishing in situ combustion, particularly, by inverseair injection, lies in the difficulty of igniting a carbonaceous stratumcontaining producible hydrocarbons and Y propagating the resultingcombustion zone thru the stratum without the fire being extinguished. Ifthe stratum contains a high percentage of heavy hydrocarbon material,such as in a tar sand, igniting by direct injection of air thru theignition borehole with application of heat thereto by any conventionalmeans risks the plugging of the stratum by driving the liquefiedsemisolid and solid hydrocarbon deposit thru the stratum away from theborehole where it is cooled and congeals. While ignition by directinjection thru the heated borehole is much more effective in igniting acarbonaceous stratum the risk of plugging off the stratum andextinguishing of the fire front in many applications of the in situcombustion process is too great and is to be avoided. On the other handit has been found extremely difficult to ignite the stratum adjacent anignition borehole by passing inversely injected air thru the stratuminto the hot ignition borehole from one or more offset boreholes.

Another problem in the recovery of hydrocarbons from a carbonaceousdeposit in a sand or rock stratum by inverse air injection comprisesdisintegration of the sand structure around the production borehole thruwhich the hot combustion gases and produced hydrocarbons pass in aninverse burning process. The sand or spalled rock fills up the boreholeand/ or is produced or entrained in the produced gases, therebyincreasing the problem of separation and recovery of hydrocarbonmaterial from the effluent gas stream.

This invention is directed to a process for igniting a carbonaceousstratum and producing hydrocarbons therefrom by inverse air injectionwhich overcomes the problems set forth in the preceding paragraphs.

Accordingly, it is an object of the invention to provide a process forigniting a carbonaceous stratum by injecting combustion supporting gasthru the stratum into an ignition borehole. Another object is tosimultaneously ignite at carbonaceous stratum around a borehole thereinand begin the movement of the resulting combustion or fire front thruthe stratum by counterflow injection of combustion supporting gaswithout resorting to direct injection thru the ignition borehole andwithout reversing the direction of flow of said gas. A further object isto provide an improved method or process of initiating counter-flow insitu combustion which is fast, simple, and certain. It is also an objectof the invention to prevent borehole caving and plugging and entrainmentof sand and spalled rock in an inverse in situ combustion process. Otherobjects will become apparent upon consideration of the accompanyingdisclosure.

A broad aspect of the invention comprises loosely packing coarseaggregates of porous refractory material in an ignition borehole withina carbonaceous stratum, the porous material being soaked or saturatedwith a heavy liquid hydrocarbon fuel either before introduction into theborehole 0r thereafter by any suitable means, igniting the fuel in thepacked mass and burning the same by inverse injection of combustionsupporting gas thru the stratum into the borehole so that the combustionin the fuel pack expands throughout the same and ignites the adjacentcarbonaceous stratum and establishes a fire front therein which movesaway from the ignition borehole countercurrently to the flow ofcombustion-supporting gas. In this manner the inverse in situ combustionprocess is initiated and can be continued by merely continuouslyinjecting combustion supporting gas into the stratum thru one or moreoffset injection boreholes therein. The process is applicable to any ofthe conventional Well patterns, such as the S, 7, or 9-spot pattern inwhich a ring of injection boreholes surrounds a central ignition andproduction borehole, or the line drive process in which a combustion orfire front is moved away from a ring of ignition and productionboreholes to a parallel line of injection boreholes on either or bothsides of the line of ignition boreholes.

The simplest method of igniting the fuel pack in the ignition boreholecomprises dropping a fusee or other incendiary device down the boreholeonto the top of the pack and injecting combustion supporting gas thruthe stratum into the pack and up through the borehole so that acombustion zone or fire front is established in the top of the fuel packand is caused to migrate downwardly therethrough and also into thecarbonaceous stratum contiguous to the fuel pack, thereby initiating thesi-tu combustion of the stratum.

It is also feasible to pack the saturated refractory material around anaxial perforate pipe or tubing which is imperforate above the pack sothat ignition of the fuel pack can be effected at the center or axisthereof and the combustion zone can then be advanced radially outwardlyto contact the stratum at the borehole wall simultaneously aoaaaas atsubstantially all points along the stratum. In utilizing this method,the perforate pipe must either be fabricated of refractory ceramicmaterial or of an alloy which stands extremely high temperatures.Another method of igniting the fuel pack axially thereof from top tobottom is to suspend an incendiary device in the form of a rope orcylinder axially within the borehole opposite the stratum and pack thefuel around the incendiary material so that by passing combustionsupporting gas thru the stratum into the fuel pack and igniting theincendiary material the same burns as a fuse throughout the length ofthe pack and ignites the fuel which is in contact with the combustionsupporting gas stream.

It has been found that with certain types of fuel the combustion zonecannot be moved through the fuel pack by countercurrent injection of airalone. In order for the fire front to be moved through the fuel pack byinverse air injection as the combustion-supporting gas, the fuel must bea heavy liquid hydrocarbon fuel which contains a substantial proportionof hydrocarbons boiling below the ignition temperature of the fuel inthe well bore, which is about 500 F. To illustrate, either asphalt ordiesel fuel, alone, does not permit inverse propagation of thecombustion front thru the fuel pack using inverse air, alone, but amixture of these fuel components in the proportion of 40 to 60 volumepercent of diesel fuel and 60 to 40 percent of asphalt permits easypropagation of the combustion front thru the pack countercurrently toinjected air. Air alone is successful in moving the combustion frontthru the fuel pack if the heavy hydrocarbon fuel contains about 3 topercent of volatile material boiling below about 500 F.

However, it is feasible to ignite a fuel pack containing diesel oil orother heavy liquid hydrocarbon of wide boiling range either at the topof the pack or axially thereof and move the resulting combustion frontthru the pack into the stratum by admixing with the injected air asuitable hydrocarbon fuel, such as propane or liquefied petroleum gases,in a concentration of about 1 to 3 or 4- volume percent. Since it isdifficult in some strata to est-ablish a combustion front around anignition borehole with inversely injected air, alone, the incorporationof fuel gas in the combustion-supporting gas also facilitatesestablishing the combustion front in the stratum and moving the sametherethrough countercurrently to the injected gas. It has also beenfound that incorporation of about 1 to 2 or 3 volume percent of fuel gas(propane) in the injected air in an inverse in situ combustion processmaterially increases the rate of movement of the front through thestratum and also materially increases the amount of hydrocarbonsproduced in the process. It is therefore highly advantageous to injectwith the inverse air a small concentration of fuel gas in that itassists in movement of the combustion zone both thru the fuel pack andthrough the stratum and assures the advantages of faster, as well asincreased, recovery of hydrocarbons.

When utilizing a mixture of diesel oil and asphalt in a fuel packcomprising porous alumina fire brick coarsely ground to about one-halfinch diameter pieces, propagation of the combustion front could beeffected utilizing air velocities in the range of about 1270 to 2950feet per hour. This range of air velocity was found by packing thecoarse fire brick saturated with a mixture of equal parts of diesel oiland asphalt (1.0362 specific gravity and 53 penetration) into a l%-inchVycor tube and igniting one end while passing air through the tube fromthe other end. It was in this manner that it was found that a fire frontor combustion zone could not be propagated thru the fuel packcountercurrently to the air stream utilizing diesel oil, alone, no doubtbecause of the too volatile nature of the diesel oil. It was also foundthat where the fuel in the pack was a mixture of paraffin wax and carbonblack, propagation could not be effected by air, alone, probably becausethe fuel in the pack was not volatile enough.

Two successful field tests were made in a tar sand lying about 50 :toabout feet below ground. In the first test a virgin ignition well borewas packed with coarse fragments of porous alumina fire brick saturatedwith a 50-5() solution of asphalt in diesel fuel and ignited by means ofa fusee dropped down the. casing. Propane-air premix containing from 1to 3 percent by volume of propane was then injected into two offsetin-line walls. In this manner a counterfiow combustion front wasestablished in the tar sand and sustained for about two days at whichtime the burning was intentionally terminated by stopping air injection.

The second test involved the re-ignition of the same zone in which thecombustion had just been extinguished.

After the original ignition well had been cooled by water injection,three gallons of diesel fuel were added and the well was shut in toallow the liquid to penetrate through the alumina-packed well bore. Thewell was again ignited with a fusee, and propane-air premix injectionwas resumed at the offset wells. A counterfiow combustion zone, feedingon injected fuel alone, Was re-established in the formation withoutdifiiculty. The new front appeared to travel outward more rapidly fromthe ignition Well than the original front, probably because of thepreheated rock which it encountered.

Any porous ceramic refractory material in coarse particulate form may beused in the process. Such materials as alumina, silica-alumina, mullite,silica (alone) and other highly refractory minerals in the form ofporous aggregates are operable in the fuel pack.

In application of the process to thick strata, it may be advantageous toutilize a fuel pack which does not completely fill the borehole withinthe stratum to be ignited and produced. Where the pressure drop thru thefuel pack is undesirably large the packing of the borehole only part wayup to the top of the stratum, such as in the range of /3 to 73 of thedepth or thickness of the stratum, reduces the pressure drop and at thesame time is effective in preventing spalling and caving of the sides ofthe borehole in the packed area, while spalling which occurs above thepack does not plug the borehole or increase the pressure drop thru thepack because the velocity of the produced gases above the fuel packentrains these particles of sand and rock. The depth of the fuel pack inrelation to the stratum will depend upon the permeability profile of thestratum, the well diameter, and the maximum size of partciles to beentrained out of the Well. These factors allow calculation of theportion of the well to be filled with the refractory fuel pack. Thisembodiment of the invention does not entirely prevent production of sandand debris but it does prevent gradual accumulation of sand and pluggingof the bottom of the well. Since sand production is usually a majorproblem only in the early stages of combustion this aspect of theinvention is a satisfactory method of ignition which does preventplugging of the well with debris.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

1 claim:

1. A process for igniting a carbonaceous stratum adjacent an ignitionborehole therein and reducing borehole caving and spalling whileproducing hydrocarbons therefrom, which comprises positioning in saidborehole a mass of porous refractory solids saturated with a heavyliquid fuel; burning said liquid fuel in said ignition borehole byigniting same and passing combustion-supporting gas consistingessentially of a mixture of air and fuel gas, said fuel gas being in therange of 1 to 3 volume percent of the mixture thin said stratum to saidignition borehole from at least one offset injection borehole, there byigniting said stratum and establishing a fire front therein; thereaftercontinuing the injection of said gas so as to advance the resulting firefront thru said stratum countercurrently to the flow of said gas; andrecovering t-hru said ignition borehole hydrocarbons produced by thecombustion.

2. The process of claim 1 wherein said liquid fuel comprises dieselfuel.

3. The process of claim 1 wherein said mass of solids is coextensivevertically with said stratum.

4. The process of claim 1 wherein said mass of solids extends from thebottom of said ignition borehole a distance in the range of /3 to /a ofthe thickness of said stratum.

5. The process of claim 1 wherein said heavy liquid fuel is a wideboiling range hydrocarbon of which 3 to 5% by volume boils below about500 F.

6. The process of claim 1 wherein said fuel gas is propane.

7. The process of claim 1 wherein said stratum is a tar sand and same isproduced by inversely injecting about 1 to 3 volume percent of fuel gaswith air.

8. The process of claim 2 wherein said liquid fuel also contains asphaltin the range of 40 to 60 weight percent of said lquid fuel.

9. A process for re-igniting a carbonaceous stratum thru a firstborehole from which a fire front has been moved into said stratum towarda second borehole therein so as to leave a denuded burned out areabetween said fire front and said first borehole and wherein thetemperature at said fire front has fallen below a combustion-supportinglevel so that combustion is terminated, which comprises igniting andburning in said first borehole a heavy liquid hydrocarbon fuel absorbedin a mass of porous refractory solids by feeding combustion-supportinggas thereto to heat said borehole to ignition tem perature of thehereinafter defined mixture; passing a combustible mixture of fuel gasand air in which said fuel gas is in the range of 1 to 3 volume percentfrom said injection borehole thru said stratum and the former fire frontto said production borehole so as to establish a combustion zone in thewall of said production borehole; and continuing the injection of saidmixture as move said hot combustion zone thru the denuded stratum to thelocus of said former fire front and into the unburned stratum so as toreignite the carbonaceous material in said stratum and reestablish thefire front therein.

10. The process of claim 9 wherein said liquid fuel is ignited at thetop of said mass and the resulting combustion zone is moved downwardlythru said mass.

References Cited in the file of this patent UNITED STATES PATENTS2,670,047 Mayes et al Feb. 23, 1954 2,793,696 Morse et a1. May 28, 19572,880,803 Parker Apr. 7, 1959 2,901,043 Campion et al Aug. 25, 1959UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,048,223 August 7, 1962 Carl J. Helmers It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 6, line 12, for "as" read so as to Signed and sealed this 3rd dayof September 1963.

(SEAL) Attest:

ERNEST w. SWIDER DAVID DD Attesting Officer Commissioner of Patents

1. A PROCESS FOR IGNITING A CARBONACEOUS STRATUM ADJACENT AN IGNITIONBOREHOLE THEREIN AND REDUCING BOREHOLE CAVING AND SPALLING WHILEPRODUCING HYDROCARBONS THEREFROM, WHICH COMPRISES POSITIONING IN SAIDBOREHOLE A MASS OF POROUS REFRACTROY SOLIDS SATURATED WITH A HEAVYLIQUID FUEL; BURNING SAID LIQUID FUEL IN SAID IGNITION BOREHOLE BYIGNITING SAME AND PASSING COMBUSION-SUPPORTING GAS CONSISTINGESSENTIALLY OF A MIXTURE OF AIR AND FUEL GAS, SAID FUEL GAS BEING IN THERANGE OF 1 TO 3 VOLUME PERCENT OF THE MIXTURE THRU SAID STRATUM TO SAIDIGNITION BOREHOLE FROM AT LEAST ONE OFFSET INJECTION BOREHOLE, THEREBYIGNITING SAID STRATUM AND ESTABLISHING A FIRE FRONT THEREIN; THEREAFTERCONTINUING THE INJECTION OF SAID GAS SO AS TO ADVANCE THE RESULTING FIREFRONT THRU SAID STRATUM COUNTERCURRENTLY TO THE FLOW OF SAID GAS; ANDRECOVERING THRU SAID IGNITION BOREHOLE HYDROCARBONS PRODUCED BY THECOMBUSTION.